I need to get a rack mount UPS as I have been experiencing power-losses recently, which are usually very rare in London. Someone I know said that people are stealing the copper for its scrap value, but I don't know what he was on about.

I do not want to get one which is noisy when online (using mains power). I have read that the fan comes on when they are over 40 degrees centigrade, or when over a certain load.

My servers idle at around 120W x2 and 40W x1, so I think a 750W model would be more than powerful enough. The 1U units are too deep for my rack, so I have shortlisted the following models:

SMT750RMI2USUA750RMI2U

I'm not sure how these differ, as the SMT models seem to have more features, but the SUA ones are more expensive. I will also need to get a network card for the SmartSlot, which is not cheap.

As far as I know any UPS will only get loud when needed. While idling/charging the fans won't be needed but the instant you lose power they'll kick into full gear until not needed or they run out of juice.

I have read that the fans also come on when the draw from the server(s) is a certain percentage of the maximum load of the UPS, even when on mains power. Remember that power is always being supplied through it, as it regulates the AC waveform.

I think the figure is 70 or 80%, but I will make sure on the APC forums before I order (I ought to get it as soon as possible, but they are so expensive with the network card), and I'll come back here and post what I find out.

Looking at spec and pics (rear view) on the APC site for these two 230V UPS units:

The SMT750RMI2U is rated for 500 watts and 750 VA. It has RJ-45 Serial, SmartSlot, and USB interface ports (to connect to monitoring software in a PC). Surge energy rating 459 Joules. Audible noise at 1 meter from surface of unit 42.00 dBA Warranty is 3 years, 2 year for battery. Picture appears to show vent in rear, but not sure if it is a fan vent.

The SUA750RMI2U is rated for 480 watts and 750 VA. It has DB-9 RS-232, SmartSlot, and USB interface ports (to connect to monitoring software in a PC). Surge energy rating 480 Joules. Audible noise at 1 meter from surface of unit 36.00 dBA. Warranty is 2 years for unit and battery. Pciture appears to show a fan vent in rear.

Given that the SMT750RMI2U may not have fan vent in rear (although there is a vent), but is louder than the SUA750RMI2U which appears to have a fan vent, there is no guarantee that the pics are accurate.

On the equivilant 120V SMT750RM2U model (for USA), the pic does show a rear vent, but not sure if it is a fan vent, and is rated at 42.00 dBA.

42 / 36 dBA is still a lot more than the <20-25 dBA we generally expect from reasonably quiet computers. Still more bearable than the 55dBA from my 3500XL atleast (I don't use my unit because of the noise level).

42 / 36 dBA is still a lot more than the <20-25 dBA we generally expect from reasonably quiet computers. Still more bearable than the 55dBA from my 3500XL atleast (I don't use my unit because of the noise level).

Depends were you place the UPS as to whether 36 dBA is acceptable. I believe that the smaller units with no fan are rated at 45 dBA (for example: APC Back-UPS 650, 390 Watts / 650 VA), and not a problem for most people. The noise problem of the small ones without a fan is that they sometimes buzz, but that varies quite a bit from one sample (or installation) to the next. It may be the case that the ratings are worst case situations, not sure.

The difference between 36 and 55 dBA may be more than you think. 55 dBA is almost four times louder than 36 dBA (a difference of 20 dBA would be four times louder).

But sadly, as has been pointed out, even 36 db are way too loud for most of us.

36dBA is the minimum dBA rating I have seen for an APC UPS, so I guess you will have do without one. Personally, I have had several APC UPS's and I cannot hear them from where I sit. I am not sure if it has to due with where mine are placed (under a desk), or too far away (more than 1 meter used for the rating). There is also the chance that a UPS rated at 36 dBA does not actually make that much noise (for most samples).

The point is that the small rack-mounted UPS from APC (750 VA or less) does not make any more noise than the standard non-rack-mounted versions that most people purchase for home use, at least according to APC specs published on their website.

I have APC Smart-UPS 700VA Rack 3U 230V - during the battery operation there is a little war inside but even when on mains the ups humms at around 40dBa and 50hz - measured. Because my PC is dead silent during the operation i will try to dampen the UPS also. I'll post the results in a couple of days after some fighting with it.

At last, i was able to make my rack APC silent. The 2 main sources of sound in those UPSs is the transformer and the top case panel (magnetic vibration). The transformer was put on dampening heat-resistant rubber ( about 3 mm height ) and the top case panel was replaced with a sheet of plywood. Effect? The UPS is dead silent during the mains operation, while on battery the sound is still there but there is no way to silence the electronics inside without putting the dampening material on every surface and making the insides of the UPS overheat.

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